Method and apparatus for controlling blast furnaces



Jan. 13, 1953 O. J. LEONE METHOD AND APPARATUS FOR CONTROLLING BLASTFURNACS 5 sheets-sheet 1 Filed Mayv 20, 1947 )MMM .Nl .Amm

JNVENToR. OTTO J. LEONE awwuf O. J. LEONE Jan. 13, 1953 METHODl ANDAPPARATUS FOR CONTROLLING BLAST FURNACES 3 Sheets-Sheet 2 Filed May 20,1947 INI/Elvmfe.l OTTO J, LEONE .EDI L www VI OwFZOU OZ( EPNE 2,625,386METHOD AND APPARATUS FOR CONTROLLING BLAST FURNACES Filed May 20, 1947O. J. LEONE Jan. 13, 1953 3 Sheets-Sheet 3 EJ-Om O...

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Patented `an. 13, 1953 UNITED STATES PATENT OFFICE METHOD AND APPARATUSFOR CONTROLLING BLAST FURNACES Otto J. Leone, West Newton, Pa., assignorof onehalf to David P. Leone, Donora, Pa.

Application May 20, 1947, Serial No. 749,238

14 Claimsl l This invention relates generally to blast furnaces andspecifically to a method and apparatus for controlling the drop in gaspressure through the charge of stock in the furnace. It is the generalobject of the invention to obtain a smoother and more regular descent ofstock in the furnace minimum the slips which result from hanging stockand the building up of excessive pressure-drops through the stock.

The inadequacy of present methods of control to compensate for furnaceirregularities often adversely affects the regularity of stock descentthrough the furnace shaft. For example, such factors as weight of thestock column, particle size and shape, gas density, gas composition(molecular weight), degree of packing, size of furnace (area andcontours), moisture in the charge and blast, viscosity vof gases, wallfriction, blast pressure, blowing rate and blast temperature are allfactors which vary the effective voids and pressure-drop through thefurnace stock. I compensate for variations in these factors by means ofa differential pressure controller.

In a stock charge of given effective voids condition, for example,increasing the blowing rate and hot blast temperature, or either of themwill increase the pressure-drop through the stock. If this pressure-dropistoo high, hanging and slipping of the furnace charge will result, withconsequent loss in furnace efficiency, increased tendl the charge;changes in particle size due to crushing or abrasion, and differences inrate of stock descent at various distances radially from the center ofthe furnace, or because of changes in cross-sectional area of thefurnace shaft. All

' these factors affect the pressure-drop through the furnace.

At the high blowing rates now usually maintained, producing excessivepressure-drop, there is a tendency for small particles to becomesuspended when a critical velocity is exceeded. This change in liftingvelocity causes the lifting of particles whose suspension decreases thepressure-drop through the charge. Because of the unequal velocitydistribution across the area traverse of the stock, however, there is atendency to channel where the lifting velocity is highest. 'I'he lowerthe gas velocity, the less the tendency to form channels of high gasvelocity and high dust-carrying capacity. I employ a differentialpressure controller to keep the gas velocities below the criticalvelocity.

Y In present-day furnace operation, the operator is not aware of ahanging condition until an excessive pressure-drop has built up or thefurnace has slipped. Corrective action cannot, therefore, be applied intime. By my invention, using pressure-drop control, corrective actionmay be applied at the correct time to eliminate vfurnace hangings, slipsand consequent delays.

Usually, just before a hanging condition occurs in a blast furnace, theblower attempts to maintain a certain rate of blowing wind. This causesthe blast-supply pressure to increase on account of the increasedresistance to flow of gases through the voids in the stock column. Inorder to maintain the mass rate of flow of gases through the stock, thepressure-drop, and therefore, the gas velocity through the stock,increases and may reach the critical lifting velocity mentioned above ifthe conditions which will finally cause hanging persist. It is the mainobject of this invention to measure and to control the pressuredrop byone of several methods.

. Under present methods of furnace operation, the measurement of suchconditions as blast rate Y of flow and pressures below or above thestock are not sufcient indications of the action of gassolid contactwithin the furnace. Even if these Vconditions were controlled, theoccurrence of channelling with resultant change in pressuredrop throughthe column might not be detected and corrected. The measurement orcontrol of pressure-drop across the stock, in addition to themeasurement or control of such conditions as gas fiows or pressures atany particular location, provides an additional tool for obtainingbetter furnace operation. To this end, I regard the voids in the bed ofsolids in terms of an equivalent orice. That is, the furnace restrictioncould be likened to an orifice plate placed in a pipe line. If thepressure above or below the orifice be controlled to a given value, thepressure-drop for a given orifice area and ow (blowing) rate wouldremain constant. Actually, however such ideal conditions do notexist inthe blast furnace.

drop would tend to raise the pressure at the top ,y

of the furnace, to counteract which the pressurecontrol valve would tendto movek toa more open position so as to restore the pressure at the topof the furnace to the set control point. It is obvious then that, whilethe valve movement would be correct to maintain the set top pressure, itwould not compensate for the change in pressuredrop and, therefore,would not counteract the increased dust-carrying capacity due tochannelling of gases. It is a further object of this invention,

therefore, to use a differential pressure Controller `in conjunctionwith straight pressure-control means as one method of operation.

A complete understanding of the invention may be obtained from thefollowing detailed description which refers to the attached drawingsshowing various embodiments and practices contemplated by my invention.In the drawings,

Figure l is a schematic diagram showing a blast furnace and one form ofcontrol system therefor according to my invention embodying adifferential pressure controller;

Figure 2 is a similar diagram showing a modified control systemutilizing two separate pressure controllers to control the pressure-dropacross the furnace; and Y y y Figure 3 is a similar diagram showing amore complete system incorporating additional measurement and controlelements so as to eiect closer control. Y K l Figure 1 illustrates oneform of control system according to the invention applied to a blastfurnace 5 so as to permit the measurement and control of the pressuredrop through they furnace stock. A blower 6 forces air through hot-blaststoves 'i and intto the blast furnace by means of tuyeres which leadfrom the hot blast line 8. After passing through'the stock charge.the'gases 'leave the furnace by means of downcomers 9 and pass to thedust-'catcher equipment. Y For a'given blast rate, and a given state ofvoids Yin the stock, there will exist a dennite pressure drop throughthe stock. A change in any of the aforementioned factors which affectthe pressure drop will cause it to change, with consequent change in thefurnace operation which in some cases may cause derangernent of stockand gas movements. Figure l shows a control system including adifferential pressure controller l0 connected to `measure a pressuredrop that will be indicative of the stock-charge resistance and controlcorrectively a restrictive valve or valves in theflue gas mains leavingthe furnace.

The differential pressure controller 1G which may be of the proportionaltype, measures the difference between the static pressures at locationsindicated by Ii and l2, connection between the points of static pressuremeasurement 'and the measuring device being made by pipe lines `i3 andld. Alternately, this measurement can be made by connecting valvedbranch lines i5 and IB to locations closer to the stock, as for example,between any horizontal planes on the stack proper, as indicated by tapsmarked Il and I8. These last connections may be single pressure taps ormay use piezometer rings with multiple pressure connections between ringand furnace shaft so as to obtain average pressures.

The controller I0 includes automatic control means to regulate thepressure-drop between the ,locations indicated above to a predeterminedvxed value as set on the controller; this control- 'ler of which varioustypes are commercially available', "may be non-indicating, indicating,

recording .or indicating-recording. When the `pointer' of the controlleri0 deviates from the set control point or control limits, the controlmechani'sm causes corrective adjustment of a restrictive' valve I9 inthe downcomer 9 by means of a power operator 2li, this action being insuc-h a direction as to restore the pressure-drop value to the set pointor limits. Although Ifhave shown the controller and operator asseparatecomponents they may be combined into one 'integrated, self-containedunit. 4

In order` to preclude any possibility of upsetting the controller actionby slight disturbances in pressure-drop caused by movement of the largebell 2l Yduring filling operations, an` interlocking device may beincorporateduto, operate in conjunction with the above controllerfth-isinterlocking device operating from the opening and closing of the bell,andvso arranged torender the control valve inoperative by locking eitherthe valve position or the differentialhimpressed on the con-troller, orby lockingl both. This last action may be controlled by the useY of anautomatic pressure-locking valve on both the pressure lines. Referringto Figure 1, I showan interlocking switch 22 operated by a suitablemechanical connection to the Vbell rod 23, and electrically connected bya circuit 24 to electrical shut-off valves 25 on each of the pressureirnpulse lines. When the bell 2l is in theclosed position, switch 22maintains valves 25 in the pressure impulse lines open; when the bellrod 23 moves to open the bell, switch 22 cau-ses valves 25 to close soas to lock the pressures into controller lo and prevent movement of thecontroller 'pointer'or power operator 2i! that would otherwise result ifthe bell movement causedian vappreciable change'in'the gas pressure atthe top of the furnace.

u K in Figurel-I show inaddition to the interlocking valve mechanism2 l,an'interlocking relay 26 connected in circuit 2l by which controlledpower is delivered to vthe valve operator 2i); relay 2-5 may also beconnected vto'interlock 22 by circuit 2d so that the power circuit willbe opened during opening ofthe bell 2| as during charging operations. Ahot-blast controller 28, connected' by two connect-ing leads 29 to athermocouple element 30, and by means of a power circuit 3l to acold-air mixer valve and power unit 32, provides a pyrmetersystem thatwill bypass the required amount of cold'air around the heating stoves'to the tot-blast side thereof, so as to 'maintain 'the temperature ofelement 3i! substantially constant. v

Although in Figure l I show `the pressure-drop controller l0 'operatinga restrictive'valve I9 in the downco'mer leaving the furnace,v thecontroller may just as well regulatea valve in the blast main 8 leadingto the furnace or, a`bleeder and tobe described later.

-to a certain fraction of the total range.

In Figure 1 a temperature element 34 is connected by lead-s 35 to atemperature compensator which is incorporated in the differentialcontroller I0. Temperature compensation may thus be accomplished forboth hot-blast and exit-gas densities by regulating the hot-blasttemperature to a constant value and by automatically correcting thecontroller I0 by the variable exit-gas temperature. Elements 30 and 34should be reasonably close to their respective pressure taps I I and I2.As an alternate correction, element 30 could operate the compensator incontroller I il and the temperature at element 34 be maintained constantby using the top-gas constanttemperature controller 53 illustrated inFigure 3; or as also shown in Figure 3, both temperatures can becontrolled to substantially constant values.

Figure 2 illustrates another alternate method of control utilizingindividual pressure controllers 36 and 31 instead of the diiTerentialcontroller I0 shown in Figure 1, and by causing these pressurecontrollers .to operate the power operators of valves 38 and 39 locatedbelow and above the furnace stock, to maintain the static pressures atpoints I I and I2 at predetermined values as set on the controllers. Inthis manner the difference between the static pressures at these pointswill be maintained substantially constant at a value below the criticalvalue. Although Figure 2 shows the controllers operating valvesrestricting the air-blast and exit-gas lines, respectively, the methodof controlling individual pressures is not to be limited to the controlof pressure valves only but may be combined with other control functionsas mentioned, for example, where a direct measurement of diiferentialpressure is made. For example, pressure controller 36 could maintainconstant pressure at points II or Il by operating snorter valve 33, orby regulating the blower output pressure. Likewise controller 31 couldbe made to operate an atmospheric relief valve. As in the ease of thedifferential type controller, the individual controllers 36 and 3l couldincorporate gas and i air-temperature measuring and compensatingmechanisms similar to those described for use with the diiferentialpressure controller.

I may also include in the system of Figure 2 a differential-pressureindicator or recorder 40 in addition to the pressure controllers so asto afford a means of measuring directly the pressure drop across thepressure taps. In laddition this instrument may incorporate a controlmechanism to operate, for example, a third restrictive valve 4| locatedeither ahead of valve 38 or after valve 39. This last arrangement is animprovement over the method using the two pressure controllers 3B and 31only in that, by using a suitably designed differential-pressuremanometer, it is possible to use a more open scale to cover a morenarrow range of pressure-drop than would be possible otherwise. Thereason is that there are inherent limitations in industrial types ofpressure-measuring elements which limit the smallest increment ofpressure change This method, then, oiers the advantage of a Vernieradjustment in addition to the closeness of control available by themethod of Figure 2 using pressure controllers 36 and 3l only.

As compared to the method represented by Figure 1, this method oifers analternate method of compensating for density chan-ges in the air or gas.In addition to density compensation by the method just described, theauxiliary controller 40 may instead of controlling the power unit andvalve 4I control the blower speed, or a valve in the hot-blast line, orsnorter valve or. in addition to having controllers 36 and 3l operatetheir respective pressure-control valves, controller 4U could controlthe injection of cooling gases or vapors, or combustion-supporting gasessuch as oxygen into the blast furnace. Thus, although Figure 2 showsanother system for the control of pressure drop, it is not limited tothe use of the equipment shown in Figure 2. These controllers mayoperate with other equipment than valves, as illustrated in Figure 3.

With reference to the pressure compensation described in the lastparagraph, a more simple, but slightly less accurate means ofcompensating the control system is obtained by using the pressure-dropcontroller40 in Figure 2 and only one of the pressure controllers,preferably omitting the blast controller 36, since normal percentagechanges of pressure and hence density, are much less at the bottom ofthe furnace than at the top of the furnace. Where further and closerdensity compensation is desired, the hot-blast temperature may beautomatically controlled by means now commercially available, and thetop temperature may be maintained constant by use of a temperaturecontroller controlling a waterinjection spray valve located in thefurnace top as shown in Figure 3 and described in detail later. Withthis arrangement the control index of temperature controller 53 would beset at a point sumciently below the normal top-gas temperatures so thatthe cooling spray will cool the top gas to a constant predeterminedtemperature. A principal advantage of this method is Vthat it will givethe effect of temperature compensation for gas density either in thecase of the differential controller or where a gas-now measurement ismade in the gas line leaving the furnace for the purpose of metering therate of flow of gas. Another advantage from an operating point of viewis that it will eliminate one more variable in the furnace operation.

Instead of injecting spray water, in some cases where the toptemperature is very low as occurs in some of the latest modern furnaces,I propose to inject a hot or cold gas instead of water. This gas may,for example, be clean blast-furnace gas. In modern furnaces operatingunder reduced gas velocity and longer gas retention time because of theexcess height of the furnace stock, the gases are cooled to too low atemperature for best furnace operation. In this case I propose to injecta heated gas just below the stock line, and thusto raise the top gastemperature to a constant value.

Although I have described the use of a separate pressure controller anddifferential-pressure controller for density compensation of thepressure drop measurement, a pressure-compensated dierential manometermay be used in which the pressure correction is automatically madeinside the manometer in the same manner as is sometimes practiced in theart of orifice flow-metering of compressible fluids which have varyingpressures. With this ararngement the pressure compensation may beapplied to the blast air or top gas, or to some pressure tap between thetuyeres and top so as to give an average pressure correction or, againas in the case of flow-meter measurement just mentioned, anaveragingtype pressure ytube with endconneo'tions to the highandlow-pressure taps may be used.

Figure 3 shows an alternate means of furnace control by which othervariables are measured and controlled. This system may be operated withall the elements as shown or some of the nner` corrections maybeeliminated, depending upon the degree of control desired.

With the arrangement shown in Figure 3, the diierential-pressurecontroller lil may be used to directly regulate or by interlocking withother controllers may lregulate combinations of valves or othercorrective devices shown as required to maintain the pressure dropacross the furnace at desired values. For example, since the pressure`drop is aiected by humidity, density, blower speedV or volume rof air,and temperature of the blast, `the controller may regulate thesequantitiesidirectly or indirectly by interlocking or cascade operation.

vTo further describe oneV of these alternate methods for example, thecontroller iii in AFigure 3, can regulate the flow cfa coolingor heatingfluid or gas in such manner as to cause the furnace to cool or gethotter, by (c) injecting moisture into or removing moisture from theblast by directly or indirectly regulating humiditycontrolequipment ,42or., (o) regulating the cold air mixing valve 32, so as to affect thehot-blast temperatureor, (c) by combining the regulating actionso (a)and (b) into a more exible control. Regulating any or all Yof thesevariables will affect the pressure drop.

Under the scheme just described, should the pressure drop increasebecause the furnace runs too hot, for example, controller le would movethe cold-air mixing valve 32 to a more open position, or alternately,particularly if the cold-air mixing valve is too small, as is the casein many old furnaces, the controller i3 would, in addition, injectmoisture in theform oi steam or Water spray by the humidity controlequipment 42. This cooling of the blast and furnace stock will permitthe passage of greater mass rate of air through the saine voids in thestock. Alternately, the steam valve in humidity controller 42 may beused in combination with the cold-air mixing valve 32 in such mannerthat moisture will be injected only when cooling is required. Thecold-air valve 32 may be operated only to cut oli cold air so as toraise the hot-blast temperature or it may be operated in conjunctionwith moisture injection for cooling and without moisture injection whenhotter blast air is required. This means of operating two valves 'iswell known in the art of automatic control and presents no difficultyfrom an operational standpoint. As an alternate to the method ofmoisture injection or humidity control, the controller 42 can be movedcloser to the furnace stack and controller it can regulate theconditioning of the air by injecting relatively inert quenching gases toalter the chemical composition of the blast gases and cause the furnaceto become more or less heated or cooled. Nitrogenor gases high in carbonmonoxide, for example, would have a cooling eiect at the bottom oi thefurnace, while a gas composition containing carbon dioxide woulddissociate because oi the high hearth temperatures, and would tend tocool the furnace by the endothermic reaction, and would affect thepressure drop.

In recent years there has been much discussion of using oxygen to enrichthe air blast The effect of injecting oxygen to enrich the blast, I

believe, would be to increase the hearth temperature but less blastwould be required, Vif it were enriched with oxygen, to maintain a givenreducing rate Vthan if no enriching oxygen were used. 'The volume ofreactant gases corresponding to the reducing rate would be less withenriched blast thanwith ordinary blast with normal oxygen, so that thepressure-drop through-the furnace 'may be considerably decreased. Thenet effect on .pressures-drop due to the hotter hearth and the :smallervolume of reactant gases will depend upon the ratio of oxygen to blastair. It can vbe seen then, that the controller l0 can be used toregulate the flow of oxygen andother "gases to maintain thepressureedrop below the Vaid the reducing action in the furnace `in the`'case of gases'rich in carbon `monoxide or hydrogen.

' Should proportional .type of control not be desired, this Acontrollermay be equipped for on-oi type of control 'so as to give correctiveaction only when the pressure diierential reaches predetermined limitsabove or below the predetermined point. It can be seen that this type ofcontrol would not necessarily be continuous and might be advantageouswhere a steam saving is desired at the sacrifice of some controlaccuracy.

In case temperature compensation for density changes is desired, as whenit is desired to obtain more accurate blast-air or exit-gas ilows, thismay be accomplished by maintaining the temperature constant as bycontrolling the hot-blast temperature by use of the hot-blast controllerand a cold-.air mixing valve, or by cooling the top-gas temperature to aconstant lower value than would otherwise normally exist.Alternately,.as in the case of pressure-compensation, atemperature-sensing device can transmit a loading .force or impulse to atemperature-compensated diierential-pressure manometer similar to thatwhich .was described for pressure cornpensation but having thecompensation linkages inverted. -Such measuring instruments arecommercially available and are fairly standard.

In the 'same manner a sample of hot blast or discharge gases can bepiped to a density or specific-gravity meter which in turn may apply acompensating loading force or pressure impulse to the compensateddiierential-pressure controller.

Referring to Figure 3, the pressure-dinerential controller I0 isconnected by pipe lines I5 and I6 to measure the pressure-drop acrossthe furnace, as between taps il and I8. This controller can operatevalve power units 3i! or 20 or 4l, being interlocked by suitabletransfer switches and interlocks 43 through 46, so that it may operateany of the valves. If it is desired, controller I0 may operate eitherthe blast-air conditioning controller 42 or the blower-volume controller41 by suitable setting of the transfer switch 43 and similar switches 48and 49.

The electrical interlock switch 22 serves during opening of the bells toprevent the controller l0 from operating valves during this period.Circuit 24 connects switch 22 with power-operated valves 25 andinterlocks 50, 5I and 52.

A top-gas temperature controller 53 is connected to a sensitive detector34. Controller 53 is interlocked with controller l0 through interlock 43so that it may operate valve 54 supplying spray nozzles 55 or, ifdesired, correct the controller I for temperature Variations.

An absolute humidity controller 56 operates from measuring mechanism 51through two connections 58 and by means of connections 59 sendscorrecting impulses to humidity controllerv 42.

An air-blast flow-meter controller 60 shown also in Figure 1 measuresair flow through a primary metering element by means of pipe lines 6land operates the regulator 4l on the blowing engine by means ofcorrecting impulse line 62. Controller I0 and controller 60 can beinterlocked for cascade operation, as indicated by line 63.

A gas-volume controller E4 measures gas flow by means of a primaryflow-metering element in downcomer 9 and impulse lines 65. If desired,it can operate valve operator 4I by means of impulse-correcting line 66or, alternately, by means of interlock connection 61, and settingtransfer switches 43 and 46 as required, it can be operated in cascadewith controller I0.

A top-pressure controller 68 is provided in case a non-compensateddifferential-pressure controller is used, to measure the gas pressure indowncomer 9 and operate Valve I3 as required to keep the gas pressureconstant at the top of the furnace.

A hot-blast temperature controller 69 operates from thermocouple 30 andcircuit 29. Correcting impulses may be sent to either cold-air mixervalve 32 over circuit 3l, or over a circuit 104for cascade connection tocontroller lo by proper setting of-transfer switches 43 and 45.Temperatureand pressure-compensation mechanisms are usually incorporatedin the differential-pressure controllers and controller I3 may be eitheran uncompensated or a pressure-compensated instrument. No extra outsidepressure-impulse lines are needed since one or the other of the twopressure lines l5, I6 would also operate the pressure compensator.

As an alternate method of gas-density control a specific-gravitycontroller may be used to correct the differential controller fordensity change by applying a loading impulse, such as an air pressure toa compensating element in the differential controller I0. Thespecic-gravity controller would be used as an alternate to apressure-compensated controller where ner corrections are desired thanis possible with temperature or pressure correction only.

It will be appreciated that the various permutations and combinationsdescribed above affect the actual gaseous flow, without referral tostandard conditions, in one or more parts of the new system by means ofwhich the pressuredrop is controlled and maintained at a constant valueor otherwise below the critical differential pressure value. Thus, achange in the gaseous flow at any particular part may impart acorrective change in the actual volume or in the rate of flow or in acombination of the two in such one or more parts of the new system.

Although I have confined my description to the iron blast furnace it isto be understood that pressure-drop control can be applied equally wellto non-ferrous smelting furnaces which are similar to the iron blastfurnace, and to certain types of gas generators which resemble blastfurnaces in construction, using the same method of charging solid fueland using counter-current flow of blast air, but which do not charge anyilux or ore solids. Ihe physical principles governing the orderlydescent ofthe solid charge,

however, is the same as in the iron blast furnace.

Advantages of this controller may be summed up as follows:

1. Better furnace efliciency through more regular control of stock andgas flows, better Working furnace, less hangings, slips, andchannelling.

2. Decreased dust losses as result of less channelling and slip-s.

3. Improved fuel economy because of better gas distribution; permits useof highest possible blast temperatures and drier air on dry blastfurnaces.

4. Less trouble due to poor coke and fine ores. Finer ores can be usedthan are now being used and with less attention to sizing.

5. Automatic control anticipates slips and applies corrective action intime, as contrasted to corrective measures being applied after slipoccurs as under manual control methods.

6. Automatic pressure-drop control, by giving better and slowergas-velocity control through the center of the furnace, will put theoperation of large-diameter furnaces on the same basisl as smal-diameterfurnaces, particularly in regard to the relative output of iron persquare foot of hearth area. Past experience indicates that mostlarge-diameter furnaces will not take as much blast per square foot ofhearth area as smaller furnaces, because of the poorer distribution ofgas velocities. Pressure-drop control will reduce this difference.

7. Increased output will be more easily obtained withdifferential-pressure control.

Although I have illustrated and described but a preferred practice andvarious embodimentsof the invention, it will be recognized thatchangesin the construction and procedure may be made without departing from thespirit of the invention or the scope of the appended' claims.

I claim:

1. In a method of operating a blast furnace or the like having a shaftrepeatedly charged with a heterogeneous stock of material, the stepscomprising, blowing a heated atmosphere upward through said stock,removing reaction gases from the top of said furnace, measuring thestatic pressure of said heated atmosphere adjacent the bottom of saidstock, measuring the static pressure of said reaction gases adjacent thetop of said stock, controlling the difference between said staticpressures to a value below that predetermined value at which saidfurnace has a tendency to generate slipping conditions therein, andeffecting said controlling by selective variation of at least one of thetemperature, pressure and rate of flow relationship-s of said heatedatmosphere and said reaction gases.

2. In a method of operating 'a blast furnace system having a hearth, ab'osh and a stack', means for supplying a heterogeneous charge of solidfuel, flux and ore adjacent the top of the stack, means for supplyingblast air under pressure adjacent the hearth, and means for taking offgaseous products adjacent the top of the stack, the steps of feedingsaid charge to the furnace, maintaining it substantially filled,substantially continuously supplying blast air, and taking off gaseousproducts, the air and evolved gaseous products traveling upwardlythrough the interstices of the stock, periodically determining thepressure drop over at least the major portion of the stack, andregulating the gaseous flow in the system in accordance with suchdetermination so as to maintain the pressure drop below a differentialconducive to disorderly downward movement ofthe stock.

said determination so as to maintain said pressure. drop below apressure differential conducive to the interruption of the orderlydownward movement of the stock.

11,. In combination with a blast furnace systern' having a hearth, abosh and a stack, means for supplying a heterogeneous charge of stockadjacent the top of the stack, means for supplyingA blast air underpressure adjacent the hearth, means for taking o gaseous productsadjacent the top of the st-ack, the apparatus comprising, pressureresponsive means connected axially across at least a substantial portionof the stack and adapted to determine the pressure drop generally acrossthe stock, and means for Varying the gaseous products from the furnacein accordance "with said determination so as to maintain said pressuredrop below a pressure differential conducive to the interruption of theorderly downward movement of the stock.

12. In combination with a blast furnacev system having a hearth, a boshand a stack, means for supplying a heterogeneous charge of stockadjacent the top of the stack, means for supplying blast air underpressure -adjacent the hearth, means for taking off gaseous productsadjacent the top of the stack, the apparatus comprising,

pressure responsive means connected axially across at least asubstantial portion of the stack 1 and adapted to determine the pressuredrop generally across the stack, and means for varying the pressure ofthe blast air relative to the pressure of the gaseous products inaccordance with said determination so as to maintain said pressure dropbelow a pressure diierential conducive to reaction gases from the top ofsaid furnace,y

measuring the static pressure of said blast air,

measuring the static pressure of said reaction.

gases, controlling the diierence between said static pressures to asubstantially constant value below that predetermined value at whichsaid furnace has a tendency to generate hanging and slipping conditionstherein, and e'iecting said controlling by selective variation of atleast one of the furnace humidity, gas density, blast air volume andblast air temperature relationships.

14. In a method of operating a blast furnace system having a hearth, abosh and a stack, means for supplying a heterogeneous charge of stockadjacent the top of the stack, means for supplying blast air underpressure adjacent the hearth, and means for taking off gaseous prodv,ucts adjacent the top of the stack, the steps of feeding said charge tothe furnace, maintaining it substantially lled, substantiallycontinuously supplying blast air, and taking off gaseous products, theair and evolved gaseous products traveling upwardly through the voids ofthe stock, substantially continuousiy determining the pressure drop overat least the major portion of the stack, substantially continuouslyregulating the gaseous iiow in the system in accordance with suchdetermination so as to maintain the pressure drop below a differentialvalue conducive to disorderly downward movement of the stock, andlocking the valve regulating the take-01T of said evolved gaseousproducts during said feeding of said charge.

OTTO J. LEONE.

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